Field of the Invention
The invention relates to a circuit configuration having a power semiconductor component and an apparatus for determining a current through the power semiconductor component.
FIG. 1 shows a conventional circuit configuration having a power semiconductor component which is configured as a power switch and is connected in series with a load, and having a current measuring configuration operating according to the so-called current sense principle. The power switch T1, configured as an n-channel power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) in FIG. 1, is connected in series with a load between a first and a second supply potential V1 V2. In order to detect a load current T1 through power switch T1, a second transistor T2 is provided, which is operated at the same operating point as the power MOSFET T1. In order to set the same operating points, the gate connections of the two transistors T1, T2 are connected to one another and their drain connections are likewise connected to one another. In addition, a regulating circuit having an operational amplifier OP and a third transistor T3 connected in series with the second transistor T2 is connected downstream of the source connection of the second transistor T2. Inputs of the operational amplifier OP are connected to the source connections of the power transistor and of the second transistor T2, the operational amplifier OP setting the third transistor T3, which acts as a controllable resistor, in such a way that the source potential of the second transistor T2 corresponds to the source potential of the power transistor T1. A current I2 flowing through the second transistor T2 is then proportional to the load current I1. During the production of the two transistors T1, T2 within the same production process, the proportionality factor corresponds to the ratio between the active transistor areas of the first and second transistors T1, T2.
A measurement voltage UM can be tapped off across a resistor RM connected in series with the second and third transistors T2, T3, through which resistor the measurement current I2 flows. A connecting terminal of the resistor which is remote from the third transistor T3 is connected to the second supply potential V2, which is usually a reference potential, in particular ground, for an entire circuit configuration in which the circuit illustrated is realized. The current measurement signal can then be tapped off relative to the reference potential V2.
The power switch illustrated in FIG. 1 serves as a so-called high-side switch, that is to say as a switch which is connected between the positive supply potential V1, or the higher positive supply potential, and the load. The generally known measurement principle in accordance with FIG. 1 cannot be employed, or can only be employed with considerable additional outlay, if the power switch serves as low-side switch, that is to say if the load is connected between the positive supply potential and the power switch. The source potential of the power transistor then approximately corresponds to the reference potential. In order that the source potential of the second transistor T2 serving for current measurement is likewise set to the value of the reference potential, the measuring resistor would have to be connected to a potential which is smaller than the reference potential. The provision of such a potential, which would have to be negative if the reference potential is ground, is associated with a considerable outlay on circuitry.
Furthermore, the measurement principle in accordance with FIG. 1 cannot be employed, or can only be employed with considerable additional outlay, when the potential at the source connection of the power switch becomes greater than the potential at the drain connection thereof, that is to say greater than the first supply potential. In this case, it would likewise be necessary to make available at the source of the measuring transistor a potential which is greater than the first supply potential and which would have to be at least as large as a potential induced by the inductive load at the source of the first transistor.